Nearly two weeks after superstorm Sandy slammed into the New York region, about a third of the city's financial district remains crippled, with no quick fixes in sight.

As life in much of the rest of Manhattan returns to normal, dozens of downtown office and apartment buildings remain dark, stores and restaurants are empty and the few signs of life on the streets are repair workers and the hum of generators and water pumps.

Thousands of workers and residents have had to find temporary quarters in an exodus that to some is painfully reminiscent of the aftermath of the September 11 2001 terrorist attacks.

Sandy swamped Lower Manhattan with a 14 foot storm surge that flooded streets and basements in a business district that remains the center of US finance industry. The storm, which hit just a few years after the district had bounced back from September 11 attacks, raises questions about its vulnerability to storm surges.

Some experts estimate that the cost to property owners of repairing damaged office buildings will be $5m to $30m each. Landlords of office buildings, retailers, restaurateurs and other small businesses also are suffering tens of millions of dollars in lost business and rent.

About 40 buildings, with about one third of the district's 100 million square feet of office space, were closed as of Friday, according to Jones Lang LaSalle,a real estate brokerage.

The businesses that have had to relocate operations reads like a who's who list in the world of Wall Street, including law firm Sullivan & Cromwell, brokerage firm Morgan Stanley and insurance giant AIG.

Citigroup relocated 1,800 workers from leased office space at 111 Wall Street. Fitch Ratings split its 650 downtown workers between Midtown Manhattan and Westchester County, and is having some employees work remotely from home.

Stroock & Stroock & Lavan, which had about 230 attorneys at 180 Maiden Lane, moved its attorneys to temporary space in Midtown made available by a Kirkland & Ellis, a law firm that has tangled with Stroock on some cases.

Most large landlords are protected by insurance and big law firms and banks have relied on disaster recovery sites designed to keep them operating. For example, a backup server outside of the city enabled Sullivan & Cromwell to keep working on Stifel Financial's planned acquisition of KBW., which was announced last week.

But it hasn't been easy. A few employees of FTI Consulting had to climb 32 floors to retrieve laptop computers at a powerless building. Some tenants are bracing for the possibility that buildings could remain closed for months or longer. "Right now it's really just one day at a time," said Margaret Chin, the City Council member who represents the area.

The cleanup is complicated by environmental issues, adding to recovery costs and delaying building owners from reopening their properties. Some flooded downtown buildings can't pump out water from their basements because the water has been contaminated from gas and oil in boilers.

New York requires landlords to report the spill and, in some cases, dispose of the water by pumping it into trucks and hauling it away. "Anyone down there with a boiler probably got hit," says Tom Elghanayan, chairman of real estate developer TF Cornerstone, which owns residential buildings downtown.

To be sure, the destruction from Sandy doesn't come close to the devastation caused by the 2001 terrorist attacks that toppled the World Trade Center. The entire financial district was closed for weeks and some tenants didn't ever return. New York City lost about $21.8bn from costs related to destroyed buildings, infrastructure and tenants who departed, according to a report from the New York City Comptroller.

In Sandy's wake, executives at many of the displaced businesses say they plan to return. Downtown civic leaders predict that the area will bounce back quickly once its buildings get pumped out.

"New York is a far more resilient place than people give it credit for," says Seth Pinsky, president of the city's Economic Development Corp.

But as downtown struggles to recover, some businesses have begun to question whether they may need to move some operations out of the area to protect them from events such as storm surges in an era of climate change.

"It definitely made me think that potentially we might need to have a second location for customer care and sales people. I'm talking about a second location in North Carolina or Florida," said Jason Richelson, founder and chief executive of ShopKeep, a technology startup that employs 33 people and was displaced from its offices at 55 Broad St.

Some residents also voiced long-term concerns about the neighbourhood. Steve Liebowitz, a 35 year old philanthropic adviser, and his wife had to climb 22 flights of stairs at their downtown apartment building. Their lease is currently up for renewal and moving elsewhere "is definitely something that is at the forefront of minds" he says.

A TF Cornerstone apartment building on Gold Street, which was still emptying water on Friday, has allowed some of its 700 displaced tenants to break their leases because the landlord can't say when they will be able to return. "I don't see how we can make them stay," says Elghanayan.

Many retailers, restaurants and other small businesses risk being put out of business if it takes months for downtown tenants to return.

Café Hanover reopened Tuesday night, but as of 8:30 Wednesday morning, it had just two customers and 11 employees inside. "There would normally have been 30 or more people in here by now," said Paul Lee, the owner.

Write to Laura Kusisto at laura.kusisto@wsj.com , Craig Karmin at craig.karmin@wsj.com and Eliot Brown at eliot.brown@wsj.com

(Erik Holm and Joshua Dawsey contributed to this article)

A version of this article appeared November 10, 2012, on page B1 in the US edition of The Wall Street Journal, with the headline: It's Déjà Vu for the Financial District : http://goo.gl/ahlvO